Anti-whaling activists say they have been outnumbered by the arrival of a 12,000 tonne Japanese icebreaker in Antarctic waters.

The Sea Shepherd Society says the Japanese ship, Shirase, arrived overnight to help whalers refuel off the coast of the Australian Antarctic Territory.

The ship is from the Japanese Maritime Self Defence Force.

Sea Shepherd director Bob Brown says one of the icebreaker's three helicopters was helping a Korean tanker gain access to the Japanese factory whaling ship, Nisshin Maru.

"It's obviously part of Japan's unfolding plan to take control...the Japanese have been moving their navy into position," he said.

Mr Brown has contacted the Australian Government, repeating calls for the Australian Navy to send support to the region.

He says the Shirase can carry up to 250 personnel, outnumbering the Sea Shepherd's 120 activists.

"There's 120 personnel all up from 24 countries including Australia and Japan but they're not armed, they don't have military wherewithal and they're now up against a giant military ship from Japan which makes any Sea Shepherd ship down there look very small indeed."

The Federal Environment Minister, Tony Burke, has been contacted for comment.